s now generally considered as incapable of definition, being a simple idea or notion received by the senses. The ancients, however, thought differently. Some of them defined it to be a passage out of one state into another; which conveys no idea to him. Motion.

who is ignorant of the nature of motion.—The Peripatetic definition has been mentioned elsewhere and shown to be wholly unintelligible, as well as their celebrated division of motion into four classes, belonging to the three categories, quality, quantity, and where; (see Metaphysics, No 188, 189, 190.) The Cartesians, too, among the moderns, pretend to define motion, by calling it a passage or removal of one part of matter, out of the neighbourhood of those parts to which it is immediately contiguous, into the neighbourhood of others. Borelli defines motion to be the successive passage of a body from place to place. Others say that it is the application of a body to different parts of infinite and immovable space; and a late writer* of uncommon acuteness has given as a definition of motion—change of place.

We have elsewhere offered our opinion of every possible attempt to define motion: but as the author of the last quoted definition has endeavoured to obviate such objections as ours, candour requires that he be heard for himself. "It is said (he observes) by some, that change implies motion, and therefore cannot be a part of its definition, being the very thing defined. To this I answer, We are speaking of the sensible idea of motion, as it appears to our sight; now changes do appear to our view, and to all our senses, which give us no idea of motion. Changes in heat or cold; in colour, flavour, smell, sound, hardness, softness, pain, pleasure; in these, and many other ideas, changes do not produce ideas like that produced by a ball rolling or a stone falling. We may perhaps ultimately trace them to motion, but to insensible motions; to motions which arise only in reflection, and constitute no part of the actual idea of change. We can therefore conceive of change, without conceiving at the same time of motion.—Change is a generic idea, including many species; motion, as a sensible idea, is a species of that genus. Change is therefore a necessary part of the definition of motion; it marks the genus of the thing defined. Motion is a change; but as there are many species of change, which of those species is motion? The answer is, It is a change of place. This marks the species; and distinguishes it from change of colour, of temperament and figure."

This is the ablest defence of an attempt to define motion that we have ever seen; and at first view the definition itself appears to be perfect. Aristotle, the prince of definers, "confiders a definition† as a speech declaring what a thing is. Every thing essential to the thing defined, and nothing more, must be contained in the definition. Now the essence of a thing consists of these two parts: first, what is common to it with other things of the same kind; and secondly, what distinguishes it from other things of the same kind. The first is called the genus of the thing; the second, its specific difference. The definition, therefore, consists of these two parts."

In obedience to this rule, the definition under consideration seems to consist of the genus, signified by the word change; and of the specific difference, denoted by the words of place. But does the speech change of place really declare what motion is? We cannot admit that it does; as, in our apprehension, a change of place is the effect of motion, and not motion itself. Suppose a lover of dialectic undertaking to define the stroke by which he saw his neighbour wounded with a bludgeon; what should we think of his art were he to call it a contusion on the head? He might say that contusion is a general term, as contusions may be produced on the arms, on the legs, and on various parts of the body; and as there are many species of contusion, if he were asked which of those species was the stroke to be defined, he might answer, "a contusion on the head." Here would be apparently the genus and specific difference; the former denoted by contusion, and the latter by the words on the head. But would this be a definition of a stroke? No, surely: a contusion on the head may be the effect of a stroke; but it can no more be the stroke itself, than a blow can be a bludgeon, or a flesh wound the point of a sword. Equally evident it is, that a change of place cannot be motion; because every body must have been actually moved before we can discern, or even conceive, a change of its place.

The act of changing the place would perhaps come nearer to a definition of motion; but so far would it be from "a speech declaring what motion is," that we are confident a man who had never by any of his senses perceived a body in actual motion, would acquire no ideas whatever from the words "act of changing place." He might have experienced changes in heat, cold, smell, and sound; but he could not possibly combine the ideas of such changes with the signification of the word place, were he even capable of understanding that word, which to us appears to be more than doubtful. (See Metaphysics, No 40, 41.)

The distinctions of motion into different kinds have been no less various, and no less insignificant, than the divisions of motion into Peripatetic division of motion into four classes, yet consider themselves as either absolute or relative. Thus we are told, that "absolute motion is the change of absolute place, and that its celerity must be measured by the quantity of absolute space which the moving body runs through in a given time." "Relative motion, on the other hand, is a mutation of the relative or vulgar place of the moving body, and has its celerity estimated by the quantity of relative space run through."

Now it is obvious, that this distinction conveys no ideas without a farther explanation of the terms by which it is expressed; but that explanation is impossible to be given. Thus, before we can understand what absolute motion is, we must understand what is meant by absolute place. But absolute place is a contradiction; for all place is relative, and consists in the positions of different bodies with regard to one another. Were a globe in the regions of empty space to be put in motion by Almighty Power, and all the rest of the corporeal world to be soon afterwards annihilated, the motion would undoubtedly continue unchanged; and yet, according to this distinction, it would be at first relative, and afterwards absolute. That the beginning of such a motion would be perceptible, and the remainder of it imperceptible, is readily granted; but on this account to consider it as of two kinds, is as absurd as to suppose the motion of the minute hand of a clock to be affected by our looking at it.

Leaving therefore these unintelligible distinctions, respecting motion, we now come to consider a question full of a very abstruse nature, but much agitated among philosophers, viz., viz. What is the original source of motion in the creation? Is it natural to matter? or are we to ascribe it to the immediate and continual agency of some immaterial being? The former has been strenuously argued by the Cartesians, and the latter by the Newtonians. The arguments of the former, founded upon the chimerical hypothesis of vortices and the original construction of matter, were evidently inconclusive; and the hypothesis of Sir Isaac Newton, who asserted that it was naturally incapable of motion, appeared more probable. To account for the quantity of motion in the universe, therefore, it became necessary to have recourse either to the Deity, or to some subordinate spiritual agent; and this became the more necessary, as the doctrine of an absolute vacuum in the celestial spaces, that is, throughout the incomparably greatest part of the creation, was one of the fundamental maxims of the system. As it was absolutely denied that matter existed in these spaces, and it was plain that the celestial bodies affected one another at immense distances, the powers of attraction and repulsion were naturally called in as the sources of motion by their impulse upon inert and sluggish matter. These being admitted, a speculation ensued concerning their nature. Spiritual, it was confessed, they were; but whether they were to be accounted the immediate action of the divine Spirit himself, or that of some subordinate and inferior spirit, was a matter of no little dispute. Sir Isaac Newton, towards the latter part of his life, began to relax somewhat of the rigidity of his former doctrine; and allowed that a very subtle medium, which he called ether, might be the cause of attraction and repulsion, and thus of the whole phenomena of nature. Since his time the multitude of discoveries in electricity, the familiarity of that fluid to fire and light, with the vast influence it has on every part of the creation with which we are acquainted, have rendered it very probable that the ether mentioned by Sir Isaac is no other than the element of fire, "the most subtle and elastic of all bodies, which seems to pervade and expand itself throughout the whole universe." Electrical experiments show that this mighty agent is everywhere present, ready to break forth into action, if not restrained and governed with the greatest wisdom. Being always restless and in motion, it actuates and enlivens the whole visible mass; is equally fitted to produce and to destroy; distinguishes the various stages of nature, and keeps up the perpetual round of generations and corruptions, pregnant with forms which it constantly sends forth and absorbs. So quick in its motions, so subtle and penetrating in its nature, so extensive in its effects, it leaveth no other than the vegetative soul or vital spirit of the world.

"The animal spirit in man is the instrument both of sense and motion. To suppose sense in the corporeal world would be gross and unwarranted; but locomotive faculties are evident in all its parts. The Pythagoreans, Platonists, and Stoics, held the world to be an animal; though some of them have chosen to consider it as a vegetable. However, the phenomena do plainly show, that there is a spirit that moves, and a mind or providence that presides. This providence, Plutarch faith, was thought to be in regard to the world what the soul is in regard to man. The order and course of things, and the experiments we daily make, show that there is a mind which governs and actuates this mundane system as the proper and real agent and cause; and that the inferior instrumental cause is pure ether, fire, or the substance of light, which is applied and determined by an infinite mind in the macrocosm or universe, with unlimited power, and according to stated rules, as it is in the microcosm with limited power and skill by the human mind. We have no proof either from experiment or reason of any other agent or efficient cause than the mind or spirit. When, therefore, we speak of corporeal agents, or corporeal causes, this is to be understood in a different, subordinate, and improper sense; and such an agent we know light or elementary fire to be."

That this elementary fire, absorbed and fixed in all Experiment-bodies, may be the cause of the universal principle of gravity, is made sufficiently evident by numberless experiments. Homberg having calcined in the focus of the burning glass some regulus of antimony, found that the impurities had gained one-tenth in weight, though the regulus, during the whole time of the operation, sent up a thick smoke, and thereby lost a considerable part of its own substance. It is vain to allege that any heterogeneous matter floating in the air, or that the air itself, may have been hurried into the mass by the action of the fire, and that by this additional matter the weight was increased; for it is known experimentally, that if a quantity of metal be even hermetically secured within a vessel of glass to keep off the air and all foreign matter, and the vessel be placed for some time in a strong fire, it will exhibit the same effect. "I have seen the operation performed (says Mr Jones) on two ounces of pewter filings, hermetically sealed up in a Florence flask, which in two hours gained 55 grains, or that is nearly one 17th. Had it remained longer in the fire, it might probably have gained something more; as, in one of Mr Boyle's experiments, steel filings were found to have gained a fourth."

Of accounting for these effects there are but two possible ways: 1. If the quantity of matter be the same, or, in the case of calcination, be somewhat less, after being exposed to the action of the fire, while the gravity of the whole is become greater; then does it follow, that gravity is not according to the quantity of matter, and of course is not one of its properties. 2. If there be an increase of the mass, it can be imputed to nothing but the matter of light or fire entangled in its passage through the substance, and so fixed in its pores, or combined with its solid parts, as to gravitate together with it. Yet it is certain, from the phenomenon of light darting from the sun, that this elementary fire does not gravitate till it is fixed in metal, or some other solid substance.—Here then we have a fluid which gravitates, if it gravitate at all, in some cases and not in others. So that whichever way forever the experiment be interpreted, we are forced to conclude that elementary or solar fire may be the cause of the law of gravitation."

That it is likewise in many cases the cause of repulsion, is known to every one who has seen it fuse metals, and convert water and mercury into elastic vapour. But there is a fact recorded by Mr Jones, which seems to evince that the same fluid, which as it issues from the sun exhibits itself in the form of light and heat, is in other circumstances converted into a very fine air, Motion or cold ether, which rushes very forcibly towards the body of that luminary. "As a sequel to what has been observed (says he) concerning the impregnation of solid substances with the particles of fire, give me leave to subjoin an experiment of M. de Stair. He tells us, that upon heating red lead in a glass, whence the air was exhausted by the rays of the sun collected in a burning glass, the vessel in which the said red lead was contained burst in pieces with a great noise. Now, as all explosions in general must be ascribed either to an admixture of the air into a rarefied space, or to what is called the generation of it; and as air was not admitted upon this occasion, it must have been generated from the calx within the vessel; and certainly was so, because Dr Hales has made it appear that this substance, like crude tartar and many others, will yield a considerable quantity of air in distillation. What went into the metal therefore as fire, came out of it again as air; which in a manner forces upon us conclusions of ineffinable value in natural philosophy, and such as may carry us very far into the most sublime part of it."

One of the conclusions which the ingenious author thinks thus forced upon us, is, that the motion of the planets round the sun, as well as round their own axes, is to be attributed to the continual agency of this fluid, under its two forms of elementary fire and pure air. As fire and light, we know that it runs with inconceivable rapidity from the body of the sun, and penetrates every corporeal substance, exerting itself sometimes with such force as nothing with which we are acquainted is able to resist. If it be indeed a fact, that this elementary fire, or principle of light and heat, afterwards cools, and becomes pure air, there cannot be a doubt, but that under such a form it will return with great force, though surely in a somewhat different direction, towards the sun, forming a vortex, in which the planets are included, and by which they must of course be carried round the centre. Mr Jones does not suppose that the air into which the principle of light and heat is converted, is of so gross a nature as our atmosphere. He rather considers it as cool ether, just as he represents light to be ether heated: but he maintains, that this ether, in its aerial form, though not fit for human respiration, is a better pabulum of fire than the air which we breathe.

This theory is exceedingly plausible; and the author supports it by many experiments. He has not, indeed, convinced us that the solar light is convertible or convertible into pure air; but he has, by just reasoning from undoubted facts, proved that the whole expanse of heaven, as far as comets wander, is filled not only with light, which is indeed obvious to the senses, but also with a fluid, which, whatever it may be called, supplies the place of the air in feeding the fire of these ignited bodies.

That the motion of the heavenly bodies should result from the perpetual agency of such a medium, appears to us a much more rational hypothesis, than that which makes them act upon each other at immense distances through empty space. But the hypothesis is by no means so complete a solution of the phenomena as some of its fond admirers pretend to think it. This fluid, whether called ether, heat, light, or air, is still material; and the question returns upon him who imagines that it is sufficient to account for gravitation, repulsion, magnetism, and cohesion, &c. "What moves the fluid itself, or makes the parts of which it is composed cohere together?" However widely it may be extended, it is incapable of positive infinity; and therefore may be divided into parts separated from each other; so that it must be held together by a foreign force, as well as a ball of lead, or a piece of wax. As matter is not essentially active, the motion of this ether, under both its forms, must likewise be considered as an effect, for which we do not think that any propelling power in the body of the sun can be admitted as a sufficient cause. For how comes the sun to possess that power, and what makes the fluid return to the sun? We have no notion of power, in the proper sense of the word, but as intelligence and volition; and, by the pious and excellent author of the Essay on the First Principles of Natural Philosophy, we are certain that the sun was never supposed to be intelligent.

Bishop Berkeley, who admits of light or ether as it is there-the instrumental cause of all corporeal motion, gets rid of this difficulty, by supposing, with the ancients, that some sup-posed to be this powerful agent is animated. "According to the animated Pythagoreans and Platonists (says his Lordship*), *Spirit, there is a life infused throughout all things; the πνεῦμα, νεῦρον, νεῦρον, νεῦρον, an intellectual and artificial fire, an inward principle, animal spirit, or natural life, producing and forming within, as art doth without; regulating, moderating, and reconciling the various motions, qualities, and parts of this mundane system. By virtue of this life, the great masses are held together in their ordinary courses, as well as the minute particles governed in their natural motions, according to the several laws of attraction, gravity, electricity, magnetism, and the rest. It is this gives inclination, teaches the spider her web, and the bee her honey. This it is that directs the roots of plants to draw forth juices from the earth, and the leaves and cortical vessels to separate and attract such particles of air and elementary fire as suit their respective natures."

This life or animal spirit seems to be the same thing which Cudworth calls plastic nature, and which has been considered elsewhere. (See Metaphysics, No 200, and Plastic Nature.) We shall therefore dismiss it at present, with just admitting the truth of the bishop's position, "that if nature be supposed the life of the world, animated by one soul, compacted into one frame, and directed or governed in all its parts by one supreme and distinct intelligence, this system cannot be accused of atheism, though perhaps it may of mistake or impropriety."

A theory of motion somewhat similar to that of Berkeley, though in several respects different from it, was not many years ago stated with great clearness, and supported with much ingenuity, in An Essay on the Powers and Mechanism of Nature, intended to improve, and more firmly establish, the grand superstructure of the Newtonian system. Mr Young, the author of the essay, admits with most other philosophers of the present age, that body is composed of atoms which are impenetrable to each other, and may be denominated solid. These atoms, however, he does not consider as primary and simple elements, incapable of resolution into principles: Motion.

He then proceeds to combat, which he does very successfully, the arguments by which the more rigid Newtonians endeavour to prove that a body in motion will continue to be moved by its own inertia, till swept by some opposite force. Having done this, he establishes the contrary conclusion by the following syllogisms:

"I. Whatever requires an active force to stop its motion, is disposed to move. Every body in motion requires an active force to stop its motion: Therefore every body in motion is disposed to move.

II. Whatever is disposed to motion is possessed of action. But a body in motion is disposed to continue in motion: Therefore a body in motion is possessed of action.

Thus it appears, that the middle part of any motion is action equally with the beginning.

"The last part of motion is its termination. It is admitted that all motion is terminated by an action contrary to the direction of the motion. It is admitted, too, that the moving body acts at the time its motion is destroyed. Thus the beginning and the end of any uniform motion are confessed to be actions; but all the intermediate continuation which connects the beginning with the end is denied to be action. What can be more unaccountable than this denial? Is it not more consonant to reason and analogy, to ascribe to the whole continued motion one uninterrupted action? Such a conclusion true philosophy, we think, requires us to make.

"To move or act, is an attribute which cannot be conceived to exist without a substance. The action of a body in motion is indeed the attribute of the body, and the body relatively to its own motion is truly a substance, having the attribute or quality of motion. But the body being a name signifying a combination of certain ideas, which ideas are found to arise from action (see PLASTIC Nature), that action which is productive of those ideas whose combination we denominate body, is of the nature of an attribute so long as it is considered as constituted of action.—To this attribute we must necessarily assign its substance. The actions which constitute body must be actions of something, or there must be something which acts. What then is this ACTIVE SOMETHING, from whose agency we get the idea of body, or whose actions constitute body? Is it not sufficient that it is something active? A name might be surely given it, but a name would not render the idea more clear. Its description may be found in every sensation; it is colour to the eye, flavour to the palate, odour to the nose, sound to the ear, and feeling to the touch; for all our sensations are but so many ways in which this ACTIVE SOMETHING is manifested to us. A substratum of solidity philosophers have imagined to exist, and have in vain sought to find. Our ACTIVE SUBSTANCE is the substratum so long sought for, and with so little success. We give it a quality by which it may be perceived; it ACTS. One modification of action produces MATTER, another generates MOTION. These modifications of action are modes of the active substance, whose presence is action: matter and motion constitute..." constitute the whole of nature. There is therefore throughout nature an active substance, the constituent essence of matter, and immediate natural agent in all effects."

By an argument which we do not think very conclusive, our author determines this active substance to be unintelligent. "In our sensations individually, not discovering (says he) the traces, not seeing the characters of intelligence, but finding only action present and necessary, our inferences go no farther than our observations warrant us to do; and we conclude in all these things an action only, and that action unintelligent." Having given our opinion of real agency elsewhere (see Metaphysics, No. 118.), we shall not here stop to examine this reasoning.—We may however ask, Whether all our sensations individually be not excited for a certain end? If they be, according to our author's mode of arguing in another place, the exciting agent should be an intelligent being. By this we are far from meaning to deny the reality of a secondary or instrumental cause of sensation which is destitute of intelligence. We are strongly inclined to think that there is such a cause, though our persuasion results not from this argument of our author's.

In our opinion, he reasons better when he says, "that a subordinate agent constructed as the matter of creation, invested with perpetual laws, and producing agreeably to those laws all the forms of being, through the varieties of which inferior intelligences can, by progressive steps, arrive ultimately at the supreme contriver, is more agreeable to our ideas of dignity, and tends to impress us with more exalted sentiments, than viewing the Deity directly in all the individual impressions we receive, divided in the infinity of particular events, and unlawful, by his continual presence in operations to our view insignificant and mean."

This active substance, or secondary cause, our author concludes to be neither matter nor mind. "Matter (says he) is a being, as a whole quiescent and inactive, but constituted of active parts, which resist separation, or cohere, giving what is usually denominated solidity to the mass. Mind is a substance which thinks. A being which should answer to neither of these definitions, would be neither matter nor mind; but an immaterial, and, if I may so say, an immental substance." Such is the active substance of Mr Young, which, considered as the cause of motion, seems not to differ greatly from the plastic nature, hyalarchical principle, or vis genitrix, of others. The manner in which it operates is indeed much more minutely detailed by our author than by any other philosopher, ancient or modern, with whose writings we have any acquaintance.

"Every thing (he says) must be in its own nature either disposed to rest or motion; consequently the active substance must be considered as a being naturally either quiescent or motive. But it cannot be naturally quiescent; for then it could not be active, because activity, which is a tendency to motion, cannot originate in a tendency to rest. Therefore the active substance is by nature motive, that is, tending to motion. The active substance is not solid, and does not resist penetration. It is, therefore, incapable of impelling or of sustaining impulse. Whence it follows, that as it tends to move, and is incapable of having its motion impeded by impulse, it must actually and continually move: in other words, motion is essential to the active substance.

"In order that this substance may act, some other thing upon which it may produce a change is necessary; for whatever suffers an action, receives some change. The active substance, in acting on some other thing, must impart and unite itself thereto; for its action is communicating its activity. But it cannot communicate its activity without imparting its substance: because it is the substance alone which possesses activity, and the quality cannot be separated from the substance. Therefore the active substance acts by uniting itself with the substance on which it acts. The union of this substance with bodies, is not to be conceived of as a junction of small parts intimately blended together and attached at their surfaces; but as an entire diffusion and incorporation of one substance with another in perfect coalescence. As bodies are not naturally active, whenever they become so, as they always do in motion, it must be by the accession of some part of the active substance. The active substance being imparted to a body, penetrates the most solid or resisting parts, and does not reside in the pores without, and at the surfaces of the solid parts. For the activity is imparted to the body itself; and not to its pores, which are no parts of the body: therefore if the active substance remained within the pores, the cause would not be present with its effect; but the cause would be in one place and the effect in another, which is impossible.

"Bodies by their impulse on others lose their activity in proportion to the impulse. This is matter of observation. Bodies which suffer impulse acquire activity in proportion to the impulse. This also is matter of observation. In impulse, therefore, the active substance passes out of the impelling body into the body impelled. For since bodies in motion are active, and activity consists in the presence of the active substance, and by impulse bodies lose their activity, therefore they lose their active substance, and the loss is proportional to the impulse. Bodies impelled acquire activity; therefore acquire active substance, and the acquisition is proportioned to the impulse. But the active substance lost by the impelling body ought to be concluded to be that found in the other; because there is no other receptacle than the impelled body to which the substance parted from can be traced, nor any other source than the active body whence that which is found can be derived. Therefore, in impulse, the active substance ought to be concluded to pass from the impelling body to the body impelled. The flowing of such a substance is a sufficient cause of the communication of activity, and no other rational cause can be assigned.

"The continued motion of a body depends not upon its inertia, but upon the continuance of the active substance within the body. The motion of a body is produced by the motion of the active substance in union with the body. It being evident, that since the active substance itself does always move, whatever it is united to will be moved along with it, if no obstacle prevent. In mere motion, the body moved is the patient, and the active substance the agent. In impulse, the body in motion may be considered as an agent, as it is made active by its active subsistence. While the active subsistence is flowing out of the active body into the obstacle or impelled body, the active body will press or impel the obstacle. For while the active subsistence is yet within the body, although flowing through it, it does not cease to impart to the body its own nature, nor can the body cease to be active because not yet deprived of the active subsistence. Therefore during its passing out of the body, such portion of the active subsistence as is yet within, is urging and disposing the body to move, in like manner as if the active subsistence were continuing in the body; and the body being thus urged to move, but impeded from moving, presses or impels the obstacle.

"We see here (says our author) an obvious explanation of impulse; it consists in the flowing of the active subsistence from a source into a receptacle;" and he thinks, that although the existence of such a subsistence had not been established on any previous grounds, the communication of motion by impulse does alone afford a sufficient proof of its reality.

He employs the agency of the same subsistence to account for many other apparent activities in bodies, such as those of fire, electricity, attraction, repulsion, elasticity, &c. All the apparent origins of corporeal activity serve, he says, to impart the active subsistence to bodies; "and where activity is without any manifest origin, the active subsistence is derived from an invisible source."

Our limits will not permit us to attend him in his solution of all the apparent activities in bodies; but the orbicular motions of the planets have been accounted for in so many different ways by philosophers ancient and modern, and each account has been to little satisfactory to him who can think, and wishes to trace effects from adequate causes, that we consider it as our duty to furnish our readers with the account of this phenomenon which is given by Mr Young.

The question which has been for long agitated, "Whence is the origin of motion?" our author considers as implying an absurdity. "It supposes (says he) that rest was the primitive state of matter, and that motion was produced by a subsequent act. But this supposition must ever be rejected, as it is giving precedence to the inferior, and inverting the order of nature." The subsistence which he holds to be the basis of matter is essentially active; and its action is motion. This motion, however, in the original element, was power without direction, agency without order, activity to no end. To this power it was necessary that a Law should be superadded; that its agency should be guided to some regular purpose, and its motion confine to the production of some uniform effects. Our author shows, or endeavours to show, by a process of reasoning which shall be examined elsewhere, that the primary atoms of matter are produced by the circular motion of the parts of this subsistence round a centre; and that a similar motion of a number of these atoms around another centre common to them all, produces what in common language is called a solid body; a cannon ball, for instance, the terrestrial globe, and the body of the sun, &c. In a word, he labours to prove, and with no small success, that a principle of union is implied in the revolving or circulating movements of the active subsistence.

"But we may also affirm (he says) a priori, that a principle of union is a general law of nature; because we see in fact all the component parts of the universe are united systems, which successively combine into larger unions, and ultimately form one whole." Let us then suppose the sun with all his planets, primary and secondary, to be already formed for the purpose of making one system, and the orbits of all of them, as well as these great bodies themselves, to be pervaded by the active subsistence, which necessarily exists in a state of motion, and is the cause of the motion of every thing corporeal. "If to this motion a principle of union be added, the effect of such a principle would be a determination of all the parts of the active subsistence, and of course all the bodies to which it is united, towards a common centre, which would be at rest, and void of any tendency in any direction. But this determination of all the parts of the system towards a common centre, tends to the destruction both of the motion of the active subsistence and of the system; for should all the parts continually approximate from a circumference towards a centre, the sun and planets would at last meet, and form one solid and quietest mass. But to preserve existence, and consequently motion, is the first law of the active subsistence, as of all being; and it cannot be doubted, that to preserve distinct the several parts of the solar system, is the first law given to the subsistence actuating that system. The union of the system is a subsequent law.

"When the direct tendency of any inferior law is obviated by a higher law, the inferior law will operate indirectly in the manner the nearest to its direct tendency that the superior law will permit. If a body in motion be obliquely obstructed, it will move on in a direction oblique to its first motion. Now the law of union, which pervades the solar system, being continually obstructed by the law of self-preservation, the motion of the active subsistence, and of the bodies to which it is united, can be no other than a revolving motion about the common centre of approach, towards which all the parts have a determination. But when this revolution has actually taken place, it gives birth to a new tendency, which supercedes the operation of the law of self-preservation. It has been shown, that the motion essential to the active subsistence, required to be governed by some law to give being to an orderly state of things. Now, there are motions simple and motions complex; the more simple is in all things first in order, and out of the more simple the more complex arises in order posterior. The most simple motion is rectilinear; therefore a rectilinear motion is to be considered as that which is the original and natural state of things, and consequently that to which all things tend. It will follow from hence, that when any portion of active subsistence in which the law of union operates, has in the manner above explained, been compelled to assume a revolving motion, that is, a motion in some curve; a tendency to a rectilinear motion will continually exist in every part of the revolving portion, and in every point of the curve which it describes during its revolution. And this rectilinear tendency will be a tendency to recede from the centre in every point..." Motion: point of the revolving orbit, and to proceed in a tangent to the orbit at each point. These two tendencies, if not originally equal, must necessarily in all cases arrive at an equality. For the tendency towards the centre, called the centripetal tendency, that is, the law of union, operating first, if we suppose the motion approaches the centre, the tendency to recede from it, called the centrifugal tendency, will have its proportion to the centripetal continually increased as the orbit of revolution grows less, so as ultimately to equal the centripetal tendency, and restrain the motion from its central course, at which point it will no longer seek the centre but revolve round it."

As our author holds that every atom of matter is formed by the motion of parts of the active substance, and every body formed by the motion of atoms; so he maintains, not only that the sun, moon, earth, planets, and stars, are penetrated by the same substance, but that each is the centre of a vortex of that substance, and that of these vortices some are included within others. "The subtle revolving fluid, the centre of whose vortex the earth occupies, not only surrounds but pervades the earth, and other vortices their earths, to their centres; and the earth and planets are by its revolutions carried around on their own axes. The earth is an inactive mass, and all its component masses are generally as well as collectively inactive; but the earth and all its parts have various collective and separate movements, imparted from the fluid which surrounds, pervades, and constitutes it. Being immersed together with its proper surrounding sphere or vortex in the larger sphere or vortex of the sun, it is carried thereby in a larger orbit about the sun, at the same time that by the revolution of its proper sphere it rotates on its own axis."

Such is the most complete view which our limits will permit us to give of Mr Young's theory of motion. To the philosopher who considers experiment as the only test of truth, and who in all his inquiries employs his hands more than his head, we are fully aware that it will appear in no better light than as "the baseless fabric of a vision." Even to the intellectual philosopher who is not frightened at the word metaphysics, we are afraid that such an active substance as the author contends for, will appear as inadequate to the production of the phenomena of gravitation and repulsion as the material ether of Mr Jones and his followers. A being void of intelligence, whether it be material or immaterial, quiescent or motive, cannot be the subject of law, in the proper sense of the word. The laws of which Mr Young speaks as necessary to regulate the motions of the active substance, must be mere forces, applied by some extrinsic and superior power. And since "motion, as it is essential to the active substance, is power without direction, agency without order, activity to no end;" since it is of such a nature, that from its unguided agitations there could result neither connection, order, nor harmony;" it follows that those extrinsic forces must be perpetually applied, because what is essential to any substance can never be destroyed or changed so long as the substance itself remains.

Forces producing order out of confusion, can be applied only by a being possessed of intelligence; and if the immediate and perpetual agency of an intelligent being be necessary to regulate the motions of the active substance, that substance itself may be thought superfluous, and its very existence be denied. Entia non sunt multiplicanda ab ipso necesse, is a rule of philosophizing which every man of science acknowledges to be just. And it will hardly be denied that the immediate and perpetual agency of an intelligent being upon Mr Jones's etherial fluid, or even upon the matter of solid bodies themselves, would be capable of producing every kind of motion without the instrumentality of a substance which is neither mind nor matter.

Such, we conceive, are the objections which our metaphysical readers may make to this theory. Part of their force, however, will perhaps be removed by the ingenious manner in which our author analyzes matter into an immaterial principle. But so much of it remains, that the writer of this article is inclined to believe that no mechanical account can be given of the motions of the heavenly bodies, the growth of plants, and various other phenomena which are usually solved by attraction and repulsion. In the present age, philosophers in general are strangely averse from admitting any occasion the agency of mind; yet as every effect must have a cause, it is surely not irrational to attribute such effects as mechanism cannot produce to the operation either of intelligence or instinct. To suppose the Deity the immediate agent in the great motions of the universe, has been deemed impious; and it must be confessed that very impious conclusions have been deduced from that principle. But there is surely no impiety in supposing, with the excellent bishop of Cloyne, that the fluid which is known to pervade the solar system, and to operate with restless force, may be animated by a powerful mind, which acts instinctively for ends of which itself knows nothing. For the existence of such a mind, no other evidence, indeed, can be brought than what is afforded by a very ancient and very general tradition, and by the impossibility of accounting for the phenomena upon principles of mere mechanism. Perhaps some of our more pious readers may be inclined to think that the Supreme Being has committed the immediate government of the various planetary systems to powerful intelligences, or angels, who, as his ministers, direct their motions with wisdom and foresight. Such an opinion is certainly not absurd in itself; and it seems to be countenanced by an ancient writer *, who, though not known by the name of a philosopher, knew as much of the matter as any founder of the most celebrated school.

To object to either of these hypotheses, as has been sometimes done, that it represents the government of the world as a perpetual miracle, betrays the grossest ignorance; for we might as well call the movements of the bodies of men and brutes, which are certainly produced by minds, miraculous. We do not affirm that either hypothesis is certainly true; but they are both as probable and as satisfactory as the hypothesis which attributes agency to attraction and repulsion, to a subtle ether, or to a substance which is neither mind nor matter. Were the immediate agency of intellect to be admitted, there would be no room for many of those disputes which have been agitated among philosophers, about the increase or diminution of motion. in the universe; because an intelligent agent, which could begin motion as well as carry it on, might increase or diminish it as he should judge proper. If instinctive agency, or something similar to it, be adopted, there is the same room for investigation as upon the principles of mechanism; because instinct works blindly, according to steady laws imposed by a superior mind, which may be discovered by observation of their effects. As we consider this as by much the most probable hypothesis of the two, we find ourselves involved in the following question: "If a certain quantity of motion was originally communicated to the matter of the universe, how comes it to pass that the original quantity still remains?" Considering the many opposite and contradictory motions which since the creation have taken place in the universe, and which have undoubtedly destroyed a great part of the original quantity, by what means has that quantity been restored?

If this question can be solved by natural means, it must be upon the principles of Newton; for, "in every case where quantities and relations of quantities are required, it is the province of mathematics to supply the information sought;" and all philosophers agree that Sir Isaac's doctrine of the composition and resolution of motion, though in what respects the heavenly bodies it may have no physical reality, is so mathematically just, as to be the only principle from which the quantity of motion, or the force of powers, can in any case be computed. If we choose to answer the question, by saying that the motion lost is restored by the interposition of the Deity, then we might as well have had recourse to him at first, and say that he alone is the true principle of motion throughout the creation.

Before we are reduced to this dilemma, however, it is necessary, in the first place, to inquire whether there is or can be any real diminution of the quantity of motion throughout the universe? In this question the Cartesians take the negative side; and maintain, that the Creator at the beginning impressed a certain quantity of motion on bodies, and that under such laws as that no part of it should be lost, but the same portion of motion should be constantly preserved in matter: and hence they conclude, that if any moving body strike on any other body, the former loses no more of its motion than it communicates to the latter. Sir Isaac Newton takes the contrary side, and argues in the following manner: "From the various compositions of two motions, it is manifest there is not always the same quantity of motion in the world; for if two balls, joined together by a slender wire, revolve with an uniform motion about their common centre of gravity, and at the same time that centre be carried uniformly in a right line drawn in the plane of their circular motion, the sum of the motions of the two balls, as often as they are in a right line, drawn from their common centre of gravity, will be greater than the sum of their motions when they are in a line perpendicular to that other. Whence it appears, that motion may be both generated and lost. But, by reason of the tenacity of fluid bodies, and the friction of their parts, with the weaknesses of the elastic power in solid bodies, nature seems to incline much rather to the destruction than the production of motion; and in reality, motion becomes continually less and less."

For bodies which are either so perfectly hard or so soft as to have no elastic power, will not rebound from each other; their impenetrability will only stop their motion. And if two such bodies equal to one another be carried with equal but opposite motions, so as to meet in a void space, by the laws of motion they must stop in the very place of concourse, lose all their motion, and be at rest for ever, unless they have an elastic power to give them a new motion. If they have elasticity enough to make them rebound with one-fourth, one-half, or three-fourths, of the force they meet with, they will lose three-fourths, one-half, or one-fourth, of their motion. And this is confirmed by experiments: for if two equal pendulums be let fall from equal heights, so as to strike full upon each other; if those pendulums be of lead or soft clay, they will lose all, or almost all, their motion; and if they be of any elastic matter, they will only retain so much motion as they receive from their elastic power."

Motion, therefore, being thus, in the opinion of our celebrated author, lost, or absolutely destroyed, it is necessary to find some cause by which it may be renewed. Such renovation Sir Isaac attributes to active principles; for instance, "the cause of gravity, whereby the planets and comets preserve their motions in their orbits, and all bodies acquire a great degree of motion in falling; and the cause of fermentation, whereby the heart and blood of animals preserve a perpetual warmth and motion, the inner parts of the earth are kept perpetually warmed; many bodies burn and shine, and the sun himself burns and shines, and with his light warms and cheers all things."

Elasticity is another cause of the renovation of motion mentioned by Sir Isaac. "We find but little motion in the world (says he), except what plainly flows either from these active principles, or from the command of the willer."

With regard to the destruction or positive loss of motion, however, we must observe, that notwithstanding the authority of Sir Isaac Newton, it is altogether impossible that any such thing can happen. All moving bodies which come under the cognizance of our senses are merely passive, and acted upon by something which we call powers or fluids, and which are to us totally invisible. Motion, therefore, cannot be lost without a destruction or diminution of one of these powers, which we have no reason to think can ever happen. When two pendulums rush against each other, the motion is the mere effect of the action of gravity; and that action, which in this case is the power, continues to be the very same whether the pendulum moves or moves not. Could motion, therefore, be exhausted in this case, we must suppose, that by separating two pendulums to the same distance from each other, and then letting them come together for a great number of times, they would at last meet with less force than before. But there is certainly not the least foundation for this supposition; and no rational person will take it into his head, that supposing the whole human race had employed themselves in nothing else from the creation to the present day, but separating pendulums and letting them stop each other's motion, they would now come together with less force than they did at first. Power, therefore, which is the cause Motion, is absolutely indestructible. Powers may indeed counteract one another, or they may be made to counteract themselves; but the moment that the obstacle is removed, they show themselves in their pristine vigour, without the least symptom of abatement or decay.

Whether, therefore, we reckon the ultimate source of motion to be spiritual or material, it is plain that it must be to our conceptions infinite; neither will the phenomena of nature allow us to give any other explanation than we have done: for no power whatever can lose more than its own quantity; and it seems absurd to think that the Deity would create the world in such a manner that it would ultimately become immoveable, and then have recourse to unknown principles to remedy the supposed defect. On the principle we have now just laid down, however, the matter becomes exceedingly plain and obvious. The Creator at first formed two opposite powers, the action of which is varied according to the circumstances of the bodies upon which they act; and these circumstances are again varied by the action of the powers themselves in innumerable ways upon one another, and the approach of one body to another, or their receding to a greater distance. Where these powers happen to oppose each other directly, the body on which they act is at rest; when they act obliquely, it moves in the diagonal; or if the force acting upon one side is by any means lessened, the body certainly must move towards that side, as is evident from the case of the atmosphere, the pressure of which, when removed from one side of a body, will make it move very violently towards that side; and if we could continually keep off the pressure in this manner, the motion would assuredly be perpetual. We must not imagine that motion is destroyed because it is counteracted; for it is impossible to destroy motion by any means but removing the cause; counteracting the effect is only a temporary obstacle, and must cease whenever the obstacle is removed. Nature, therefore, having in itself an infinite quantity of motion produces greater or lesser motions, according to the various action of the moving powers upon different bodies or upon one another, without a possibility of the general flock being either augmented or diminished, unless one of the moving powers was to be withdrawn by the Creator; in which case, the other would destroy the whole system in an instant. As to the nature of these great original moving powers, we must confess ourselves totally ignorant; nor do we perceive any data from which the nature of them can be investigated. The elements of light, air, &c., are the agents; but in what manner they act, or in what manner they received their action, can be known only to the Creator.

Perpetual Motion, in Mechanics, a motion which is supplied and renewed from itself, without the intervention of any external cause; or it is an uninterrupted communication of the same degree of motion from one part of matter to another, in a circle or other curve returning into itself, so that the same momentum still returns undiminished upon the first mover.

The celebrated problem of a perpetual motion consists in the inventing a machine, which has the principle of its motion within itself. M. de la Hire has demonstrated the impossibility of any such machine, and finds that it amounts to this, viz. to find a body which is both heavier and lighter at the same time, or to find a body which is heavier than itself.

Animal Motion, that which is performed by animals at the command of the mind or will.

Though all the motions of animals, whether voluntary or involuntary, are performed by means of the muscles and nerves, yet neither these nor the subtile fluid which resides in them are to be accounted the ultimate sources of animal motion. They depend entirely upon the mind for those motions which are properly to be accounted animal. All the involuntary motions, such as those of the blood, the heart, muscles, organs subservient to respiration and digestion, &c., are to be classified with those of vegetables; for though no vegetables have them in such perfection as animals, there are yet traces of them to be found evidently among vegetables, and that so remarkable, that some have imagined the animal and vegetable kingdoms to approach each other so nearly that they could scarce be distinguished by a philosophic eye. See Muscle.

Though the motions of animals, however, depend on the action of the mind or of the will, external objects seem originally to have the command of the mind itself; for unless an animal perceive something, it will not be inclined to act. By means of the ideas once received, indeed, and retained in the memory, it acquires a self-moving power, independent of any object present at the time, which is not the case with vegetables; for however they may act from a present impulse, their motions never appear to be derived from any source which may not be accounted strictly mechanical.

According to some, motion is the cause of sensation itself; and indeed it seems very probable that the motions of that subtile fluid, called light or electricity, in our bodies always accompany our sensations; but whether these be the cause, or only the medium, of sense, cannot be discovered.

Though all animals are endowed with a power of voluntary motion, yet there is a very great variety in the degrees of that power; to determine which no certain rules can be affixed; neither can we, from the situation and manner of life of animals, derive any probable reason why the motion of one should differ so very much from that of another. This difference does not arise from their size, their ferocity, their timidity, nor any other property that we can imagine. The elephant, though the strongest land animal, is by no means the swiftest in its motions; the horse is much swifter than the bull, though there is not much difference in their size; a greyhound is much swifter than a cat, though the former be much larger, and though both live in the same manner, viz. by hunting. Among insects the same unaccountable diversity is observable. The louse and flea are both vermin, are both nearly of the same size, and both feed on the bodies of animals; yet there is no comparison between the swiftness of their motions: while the bug, which is much larger than either, seems to have a kind of medium swiftness between both.—This very remarkable circumstance seems not even to depend on the range which animals are obliged to take in order to procure food for themselves: the motion of a snail is slower than that of an earthworm; while Motion. that of many caterpillars is much quicker than either; though we can scarce determine which of the three has the greatest or the least extensive range for its food.

Of all animals the shell fish move the slowest, inasmuch that some have supposed them to be entirely de-stitute of locomotive powers; and muscles particularly are denied to have any faculty of this kind. Every one knows that these animals can open and shut their shells at pleasure; and it cannot escape observation, that in every muscle there is a fleshy protuberance of a much redder colour than the rest. This has been thought to be a tongue or proboscis, by which the animal takes in its food; but is in reality the instrument of its motion from place to place. This protuberance is divided into two lobes, which perform the office of feet. When the river muscle is inclined to remove from its station, it opens its shells, thrusts out this protuberance, and digs a furrow in the sand; and into this furrow, by the action of the same protuberance, the shell is made to fall in a vertical position. It is recovered out of this into the former horizontal one, by pushing back the sand with the same tentacula, lengthening the furrow, and thus the animal continues its journey by a continual turning toplly-turvy.—Marine muscles perform their motions in the same manner, and by similar instruments. In general they are firmly attached to rocks or small stones by threads about two inches long, which are spun from a glutinous substance in the protuberances already mentioned.

Other animals which inhabit bivalved shells, perform their motions by a kind of leg or foot; which, however, they can alter into almost any figure they please. By means of this leg they can not only sink into the mud, or rise out of it at pleasure, but can even leap from the place where they are; and this can be done by the limpet, which people are apt to imagine one of the most sluggish animals in nature.—When this creature is about to make a spring, it sets its shell on edge, as if to diminish friction; then, stretching out the leg as far as possible, it makes it embrace a portion of the shell, and by a sudden movement, similar to that of a spring let loose, it strikes the earth with its leg, and actually leaps to a considerable distance.

The spout, or razor-fish, is said to be incapable of moving forward horizontally on the surface; but it digs a hole sometimes two feet deep in the sand, in which it can ascend or descend at pleasure. The leg, by which it performs all its movements, is fleshy, cylindrical, and pretty long; and the animal can at pleasure make it assume the form of a ball. When lying on the surface of the sand, and about to sink into it, the leg is extended from the inferior end of the shell, and makes the extremity of it take on the form of a shovel, sharp on each side, and terminating in a point. With this instrument the animal makes a hole in the sand; after which it advances the leg still farther into it, makes it assume the form of a hook, and with this, as a fulcrum, it obliges the shell to descend into the hole. This operation is continued until the whole shell be covered; and when the animal wishes to regain the surface, it makes the extremity of the leg to assume the form of a ball, and makes an effort to extend it. The ball, however, prevents any farther descent, and the reaction of the muscular effort raises up the whole shell, which operation is continued until it reaches the surface; and it is surprising with what facility these motions are accomplished by an animal seemingly so little qualified to move at all. Another particularity in this fish is, that though it lives among salt water, it abhors salt so much, that when a little is thrown into its hole it instantly leaves it. But it is still more remarkable, that if you once take hold of the spout-fish, and then allow it to retire into its hole, it cannot then be driven out by salt; though unless it be taken hold of by the hand, the application of salt will make it come to the surface as often as you please.

All other shell fish, even those apparently the most sluggish and destitute of any apparatus for motion, are found to be furnished with such instruments as enable them to perform all those movements for which they have any occasion. Thus the scallop, a well-known animal inhabiting a bivalved shell, can both swim upon the surface of water and move upon land. When it happens to be deserted by the tide, it opens its shell to the full extent, and shutting it again with a sudden jerk, the reaction of the ground gives such an impulse to the whole, that it sometimes springs five or six inches from the ground; and by a continued repetition of this action, it gradually tumbles forward until it regains the water. Its method of failing is still more curious. Having attained the surface of the water by means unknown to us, it opens the shell, and puts one-half above water, the other with the body of the animal in it remaining below. Great numbers of them are thus frequently seen failing in company with their shells sticking up above water when the weather is fine, and the wind acting upon them as fails; but on the least alarm they instantly shut their shells, and all sink to the bottom together.

The oyster has generally been supposed one of the most sluggish animals in nature, and totally incapable of voluntary motion; but from the researches of the Abbé Dicquemarre, this opinion seems to be erroneous. The oyster, like many other bivalved shell-fish, has a power of ejecting water out from its body; and this property may easily be observed by putting some of them into a plate with as much sea water as will cover them. The water is ejected with too much force, as not only to repel the approach of ordinary enemies, but to move the whole animal backwards or sidewise, in a direction contrary to that in which the water was ejected. It has been also supposed, that oysters are destitute of sensation; but M. Dicquemarre has shown, that they not only possess sensation, but that they are capable of deriving knowledge from experience. When removed from such places as are entirely covered with the sea, when destitute of experience, they open their shells and die in a few days; but if they happen to escape this danger, and the water covers them again, they will not open their shells again, but keep them shut, as if warned by experience to avoid a danger similar to what they formerly underwent.

The motions of the sea-urchin are perhaps more curious and complicated than those of any other animal. It inhabits a beautiful multivalved shell, divided into triangular compartments, and covered with great numbers of prickles; from which last circumstance it receives the name of sea urchin or sea hedgehog. The triangles triangles are separated from one another by regular belts, and perforated by a great number of holes, from every one of which issues a fleshy horn similar to that of a nail, and capable of moving in a similar manner. The principal use of these horns seems to be to fix the animal to rocks or stones, though it likewise makes use of them in its progressive motion. By means of these horns and pricks, it is enabled to walk either on its back or its belly; but it most commonly makes use of those which are near the mouth. Occasionally it has a progressive motion by turning round like a wheel.

The animals called sea-nettles or medusae, though extremely slow in their motions, are nevertheless evidently capable of moving at pleasure from place to place. The variety of their figure is such, that it is difficult to assign them any determinate figure whatever. In general, however, they resemble a truncated cone, the base of which is applied to the rock to which they adhere. Their colours are various, whitish, brown, red or greenish: the mouth is very large; and when opened appears surrounded with filaments resembling the horns of snails, which being disposed in three rows around it, give the animal the appearance of a flower; and through every one of these the animal has the power of squirting the sea water. The structure of these animals is extremely singular; they consisting all of one organ, viz. a stomach. When searching for food, they extend their filaments, and quickly entangle any small animals that come within their reach. The prey is instantly swallowed, and the mouth shut close upon it like a purse; in which state it remains for many days before the nutritive parts are extracted. The animal, though scarcely an inch or an inch and a half in diameter, is nevertheless so dilatable, that it can swallow large whelks and mussels, the shells of which are thrown out by the mouth after the nutritive parts have been exhausted. Sometimes the shell is too large to be voided this way; in which case the body of the animal splits, and the shell is voided through the opening, which in a short time heals up again. The progressive motion of this creature is so slow, that it resembles that of the hour hand of a clock, and is performed by means of innumerable muscles placed on the outside of the body. All these are tubular, and filled with a fluid, which makes them project like pricks. On occasion it can likewise loosen the base of the cone from the rock, and inverting its body, move by means of the filaments already mentioned, which surround the mouth; but even the motion performed in this manner is almost as slow as the other.

Some animals are capable of moving backwards, apparently with the same facility that they do forwards, and that by means of the same instruments which move them forward. The common house fly exhibits an instance of this, and frequently employs this retrograde motion in its ordinary course; though we cannot know the reason of its employing such an extraordinary method. Another remarkable instance is given by Mr Smellie in the mason-bee. This is one of the solitary species, and has its name from the mode of constructing its nest with mud or mortar. Externally this nest has no regular appearance, but at first sight is taken for a quantity of dirt adhering to the wall; though the internal part be furnished with cells in the same regular manner with the nests of other insects of the bee kind. When this bee leaves its nest, another frequently takes possession of it; in which case a battle never fails to ensue on the return of the real proprietor. The dispute is decided in the air; and each party endeavours to get above the other, as birds of prey are wont to do in order to give a downward blow. The undermost one, to avoid the stroke, instead of flying forward or laterally, always flies backward. The encounter is so violent, that when they strike, both parties fall to the ground.

Vegetable Motion. Though vegetables have not the power of moving from one place to another like animals, they are nevertheless capable of moving their different parts in such a manner as would lead us to suspect that they are actuated by a sort of instinct. Hence many have been induced to suppose, that the animal and vegetable kingdoms are in a manner indistinguishable from one another; and that the highest degree of vegetable life can hardly be known from the lowest degree of animal life. The essential and insuperable distinction, however, between the two, is the faculty of sensation, and loco-motion in consequence of it. Were it not, indeed, for the manifestation of sense by moving from one place to another, we should not be able to tell whether vegetables were possessed of sensation or not; but whatever motions they may be possessed of, it is certain that no vegetable has the faculty of moving from one place to another. Some have endeavoured to distinguish the two kingdoms by the digestion of food; alleging that plants have no proper organs, such as a stomach, &c., for taking in and digesting their aliment. But to this it has been replied, that the whole body of a vegetable is a stomach, and absorbs its food at every pore. This, however, seems not to be a sufficient answer. All animals take in their food at intervals, and there is not a single instance of one which eats perpetually. The food is also taken into the body of the animal, and application of the parts made by means of the internal organization of the viscera; but in vegetables, their whole bodies are immersed in their food, and absorb it by the surface, as animal bodies will sometimes absorb liquids when put into them. The roots of a tree indeed will change their direction when they meet with a stone, and will turn from barren into fertile ground; but this is evidently mere mechanism, without any proof of will or sensation; for the nourishment of the root comes not from the stone, but from the earth around it; and the increase in size is not owing to any expansion of the matter which the root already contains, but to the apposition of new matter; whence the increase of size must always take place in the direction from whence the nourishment proceeds. On this principle also may we explain the reason why the roots of a tree, after having arrived at the edge of a ditch, instead of shooting out into the air, will creep down the one side, along the bottom, and up the other.

In their other movements the vegetables discover nothing like sensation or design. They will indeed uniformly bend towards light, or towards water; but in the one case we must attribute the phenomenon to the action of the elements of light and air upon them; and in the latter, the property seems to be the same; with what in other cases we call attraction. Thus, if Motion. a root be uncovered, and a wet sponge placed near it in a direction different from that in which the root was proceeding, it will soon alter its position, and turn towards the sponge; and thus we may vary the direction of the root as often as we please. The efforts of a plant to turn from darkness or shade into sunshine are very remarkable; as in order to accomplish this, not only the leaves will be inclined, but even the stems and branches twisted. When a wet sponge is held under the leaves of a tree, they bend down in order to touch it. If a vessel of water be put within six inches of a growing cucumber, in less than 24 hours the latter will alter its direction; the branches will bend towards the water, and never alter their course until they come in contact with it. The most remarkable instance of this kind of motion, however, is, that when a pole is brought near a vine, the latter will turn towards it, and never cease extending its branches till it lays hold of the support.

The motions of the sensitive plant, and others of the same kind, have been considered as very wonderful; but it is doubtful if any of them be really more so than that of the vine just mentioned. None of these show any kind of propensity to move without an actual touch. A very slight one, indeed, makes the sensitive plant contract, and the whole branch, together with the leaves, bend down towards the earth.—These phenomena are by some ascribed to electricity. Even the motions of the *hedysarum gyrans*, at first sight seem so much more surprising than those of the sensitive plant, may it be supposed admit of explanation upon the same principle. The American plant called *dionaea muscipula*, or *Venus's fly-trap*, is another example of very wonderful mechanism in vegetables, though even this does not argue any degree of sensation in this plant more than in others. The leaves of the dionaea are jointed, and furnished with two rows of prickles. A number of small glands upon the surface secrete a sweet juice which entices flies to come and settle upon it; but the moment these insects touch the fatal spot, the leaves fold up, and squeeze them to death between the prickles. The leaves fold up in the same manner when the plant is touched with a straw or pin. The *drosera rotundifolia* and *longifolia*, round and long-leaved sundew, plants of our own country, not uncommon in boggy ground, possess a similar structure, and perform similar functions.

The folding up of the leaves of certain plants in the absence of the sun's light, called their *sleep*, affords another very curious instance of vegetable motion.—Almost all vegetables, indeed, undergo such a remarkable change in the night, that it is difficult to know exactly how many kinds do really sleep. They fold up their leaves in many different ways; but all agree in disposing of them in such a manner as to afford the best protection to the young stems, flower buds or fruit. The leaves of the tamarind tree contract round the young fruit in order to protect it from nocturnal cold; and those of fennel, glycinea, and many other papilionaceous plants, dispose of their leaves in the same manner. The leaves of the chickweed, *asclepias atriplex*, &c. are disposed in opposite pairs. In the night time they rise perpendicularly, and join so close at the top that the flowers are concealed by them. In like manner do the leaves protect the flowers of the fida or *althaea theo-*

phrasti*, *genothera*, *folium*, and the Egyptian vetch. All these are erected during the night; but those of the white lupine, in time of sleep, hang down.

The flowers of plants also have motions peculiar to themselves. Many of them during the night are enclosed in their calyxes. Some, particularly those of the German spurge, *geranium striatum*, and common whitlow grass, when asleep, bend towards the earth; by which means the noxious effects of rain or dew are prevented. All these motions have been commonly ascribed to the sun's rays; and Mr Smellie informs us that in some of the examples above mentioned the effects were evidently to be ascribed to heat: but plants kept in a hot-house, where the temperature of the day and night are alike, contract their leaves, and sleep in the same manner as if they were exposed to the open air; "whence it appears (says he), that the sleep of plants, is owing rather to a peculiar law, than to a quicker or slower motion of the juices." He suspects, therefore, that as the sleep of plants is not owing to the mere absence of heat, it may be occasioned by the want of light; and to ascertain this he proposes an experiment of throwing upon them a strong artificial light. "If notwithstanding this light (says he), the plants are not roused, but continue to sleep as usual, then it may be presumed that their organs, like those of animals, are not only irritable, but require the reparation of some invigorating influence which they have lost while awake, by the agitations of the air and of the sun's rays, by the act of growing, or by some other latent cause." On this, however, we must remark, that the throwing of artificial light upon plants cannot be attended with the same consequences as that of the light of the sun, unless the former were as strong as the latter, which is impossible; and even granting that we could procure an artificial light as strong as that of the sun, a difference might be occasioned by the different directions of the rays, those of the sun being very nearly parallel, while the rays of all artificial light diverge very greatly. If, therefore, we are to make an experiment of this kind, the rays should be rendered parallel by means of a burning mirror. Here again we would be involved in a difficulty; for the rays of the sun proceed all in one direction; but as of necessity we must employ different mirrors in our experiment, the light must fall upon the plant in different directions, so that we could not reasonably expect the same result as when the plants are directly exposed to the rays of the sun.

The motion of plants, not being deducible from sensation, as in animals, must be ascribed to that property called irritability; and this property is possessed infensibly by the parts of animals in a greater degree than even by the most irritable vegetable. The muscular fibres will contract on the application of any stimulating substance, even after they are detached from the body to which they belonged. The heart of a frog will continue to beat when pricked with a pin for several hours after it is taken out of the body. The heart of a viper, or of a turtle, beats distinctly from 20 to 30 hours after the death of these animals. When the intestines of a dog, or any other quadruped, are suddenly cut into different portions, all of them crawl about like worms, and contract upon the slightest touch. The heart, intestines, and diaphragm, are the most irritable... irritable parts of animal bodies; and to discover whether this quality resides in all plants, experiments should be made chiefly on leaves, flowers, buds, and the tender fibres of the roots.

The motions of plants are universally ascribed by our author to irritability, to which also we have ascribed them under the article Animal. The term, however, requires an explanation; and to give this in an intelligible manner requires some attention. The most obvious comparison is that of an electrified thread; which on the approach of any unelectrified substance, shows a variety of motions, equally surprising with those of the parts of plants or the muscular fibres cut out of the body. Could we suppose that the electricity of a thread might be preserved after it was cut off from the electrifying substance, it would show as much irritability as even the muscular fibres, or portions of the intestines of animals. We know, from the history of the torpedo, electrical eel, &c., that there are animals in which the electric fluid acts in such a manner as to produce a much more powerful effect than that of giving motion to the leaves of plants. The readiness, therefore, with which this fluid is thrown into agitations when any substance in which it acts is touched, is without doubt the irritability in question; but we have from thence no more reason to ascribe sensation to these irritable bodies, than to an electrified bottle when it discharges itself, or makes a cork ball play around it.

In a paper read before the Academy of Sciences at Paris, by M. Broussonet, the author inclines to confound irritability and sensibility together. The different parts of plants (says he) enjoy the faculty of motion; but the motions of a vegetable are very different in their nature from those of an animal: the most sensible, those that are produced with most rapidity in plants, are always influenced by some stimulating cause. Irritability, which is nothing but sensibility made manifest by motion, is a general law to which nature has subjected all living beings; and it is this that continually watches over their preservation. Being more powerful in animals than in plants, it may be often confounded in these last with phenomena that depend on a quite different cause. In the vegetable it is only the organ which is exposed to the action of the stimulating power that moves. Irritation in particular places never produces that prompt combination of sensations which we observe in animals; in consequence of which certain parts are put in motion without being directly affected, and which otherwise might have been passive.

"The more perfect the organization in the different parts of animals is, the more apparent are the signs of irritability. The parts that come nearest to those of vegetables, and in which of consequence the organization is most imperfect, are the least irritable. The same law holds with regard to plants; but the result is opposite: the signs of irritability are most sensible in proportion to the analogy of the parts with those of animals; and they are imperceptible in those that are dissimilar. This assertion is proved by what we observe in the organs destined in vegetables to perpetuate the species. Those parts alone seem sensible to stimuli; the bark, leaves, stalks, and roots showing no signs of irritability.

"The motions essentially vital, which have in plants the greatest affinity with those of animals, are the course of the sap, the passage of the air in the trachea, the different positions which the flowers of certain plants take at certain hours of the day, &c. But if we attend to the manner in which all these motions in plants are performed, we shall find that they present a greater number of modifications than the analogous motions that take place in animals. The temperature of the atmosphere, its agitation, light, &c., have great influence on the motions of plants, by accelerating or retarding the course of their fluids; and, as they cannot change their place, these variations produce in them changes more obvious and more uniform than in animals."

Our author now proceeds to inform us, that some of the motions of plants are occasioned by the rarity of the juices in plants, and others by their abundance. Of the former kind are those by which the capsules of some plants suddenly burst with a spring, and throw their seeds to some distance. Of the other kind are the action of the stamina in the parietaria, the inflection of the peduncles of flowers, and of the pistilla.

"These motions (says he) which are particularly observed in the organs destined to the reproduction of the individual, not appearing except in circumstances that render them absolutely necessary, seem in some measure to be the effect of a particular combination: they are, however, merely mechanical; for they are always produced in the same way and in the same circumstances. Thus the rose of Jericho, and the dry fruit of several species of megaphyllum, do not open but when their vessels are full of water.

"The sudden disengagement of fluids produces a kind of motion. To this cause we must attribute a great number of phenomena observable in the leaves of several plants, and which do not depend on irritability. The small glands in each leaf of the dionaea are no sooner punctured by an insect, than it instantly folds up and seizes the animal: the puncture seems to operate a disengagement of the fluid which kept the leaf expanded by filling its vessels. This explanation is the more probable, that in the early state of the vegetation of this plant, when the small glands are hardly evolved, and when probably the juices do not run in sufficient abundance, the leaves are folded up exactly as they appear when punctured by an insect at a more advanced period. We observe a phenomenon similar to this in both species of the drosera (sun-dew), mentioned above. The mechanism here is very easily observable: the leaves are at first folded up; the juices are not yet propelled into the fine hairs with which they are covered; but after they are expanded, the presence of the fluid is manifest by a drop seen at the extremity of each hair: it is by absorbing this fluid that an insect empties the vessels of the leaf, which then folds up, and resumes its first state: the promptitude of the action is proportioned to the number of hairs touched by the insect. This motion in some degree resembles that which takes place in the limb of an animal kept in a state of flexion by a tumor in the joint; when the matter which obstructed the motion is discharged, the limb instantly resumes its former position. The phenomena that depend on the abundance of fluids are particularly evident in plants which grow in wet soils; the drosera and dionaea are of this kind: and it is known by the experiments of Messrs. Du Fay and Du Hamel, that sensitive plants are particularly sensible when the sun is obscured by clouds and the air warm and moist.

The influence of external causes sometimes so modifies the vital motions in plants, that we would be tempted to ascribe them to volition, like those that depend entirely on that faculty in animals. If we set a pole in the ground near a twining plant, it always lays hold of the pole for support, in whatever place we put it. The same thing occurs in the tendrils of the vine; which always attach themselves to the support presented them, on whatever side it may be placed, provided they can reach it; but these motions are entirely vital: the twining plants and the tendrils direct themselves to every quarter, and consequently cannot fail of meeting with the bodies within their reach. These motions are performed as long as the parts continue to grow; but when they cease to elongate, if they have not been able to reach any body on which they can fix, they bend back upon themselves. This and other observations show how far the vital motions in plants may be modified by external causes, and how essentially they differ from those that are the effect of volition in animals.

"Some plants appear endowed with no sort of motion; some have leaves that can move in different directions: their motions are generally modified by different causes; but none appear so eminently possessed of this quality as the *hedysarum gyrans* of Linnæus.—No part of this plant shows any signs of irritability upon application of stimuli; and the motion of its foliæ ceases when the leaflets are agitated by the wind.—When the sun is warm, the little leaves of the *hedysarum* are also immovable; but when the weather is warm and moist, or when it rains, they move very freely. This motion seems indispensably necessary to the plant; for it begins as soon as the first leaves unfold, and continues even during the night; but in time it grows weaker. In our stoves it is most considerable during the first year; in the second, it is not very sensible: in its native place all the leaves have a motion never observed here. The moving leaflets are most agitated while the plants are in full flower, and the process of fructification goes on. The oscillatory motion is so natural to it, that it not only remains for three or four days in the leaflets of a branch that has been cut off and put in water, but is even continued though the branch be exposed to the air. The leaves seem to perform the office of the heart in vegetables. When a plant is stripped of its leaves, the progress of vegetation is arrested; and such vegetables resemble those animals which have a periodical sleep, induced by a diminution of the action of the heart. Many plants hardly show any signs of motion; many seem also wholly cataleptic; which is rarely if ever found in animals. The footstalks of the flowers of *dracoccephalum*, a Virginian plant, preserve themselves in whatever position they are placed.

Muscular Motion. See Muscle.